This invention relates to a method of preparing in a single step, a mixture comprising a p-brominated phenol and a p-benzoquinone. More particularly the method relates to a method of preparing in a single step, a mixture of p-bromophenol and p-benzoquinone intermediates which may subsequently be converted in single step transformations to hydroquinones and dihydroxy aromatic compounds useful in the preparation of polycarbonate copolymers.
A variety of copolymers possessing useful and desirable properties comprise structural units derived from both hydroquinones and 4,4xe2x80x2dihydroxybiphenyls. Examples of include the polyether sulfone (CAS No. 90337-94-3) prepared from hydroquinone (HQ), 4,4xe2x80x2-dihydroxybiphenol (BP) and bis(4-chlorophenyl)sulfone; and the polyester (CAS No. 96892-06-7) derived from HQ, BP and a mixture of iso- and terephthalic acid. Additionally, polycarbonates comprising structural units derived from HQ, BP and another bisphenol comonomer (e.g. CAS No. 491588-47-7) show promise in a variety of materials applications.
Typically, the hydroquinone derivative and the 4,4xe2x80x2-dihydroxybiphenyl derivative used in the preparation of such polymers are prepared in independent manufacturing steps. Hydroquinone is typically prepared by air oxidation and fragmentation of 1,4-diisopropylbenzene, or by direct oxidation of phenol. Typically, 4,4xe2x80x2-dihydroxybiphenyl is obtained by oxidative coupling of 2,6-di-tert-butylphenol followed by acid mediated removal of the tert-butyl groups in the coupled product. Hydroquinones may be prepared as well by hydrolysis of a p-bromophenol as illustrated in U.S. Pat. No. 1,934,656. In addition, 4,4xe2x80x2-dihydroxybiphenyls may be prepared by reductive coupling of a p-bromophenol to the corresponding 4,4xe2x80x2-dihydroxybiphenyl as described in U.S. Pat. No. 5,177,258.
Commonly assigned, co-pending U.S. application Ser. No. 10/342,475 (filed Jan. 16, 2003) discloses an efficient means of preparing a p-bromophenol as a single intermediate which can be transformed by hydrolysis or reductive coupling into either a hydroquinone or a 4,4xe2x80x2-dihydroxybiphenyl. While this approach provides additional efficiencies based upon its use of a single intermediate p-bromophenol relative to known methods, improved methods continue to be sought, especially in light of the challenges presented by the rigorous conditions required for the hydrolytic transformation of the intermediate p-bromophenol to the corresponding hydroquinone.
The present invention is related to that described in co-pending U.S. application Ser. No. 10/342,475 (filed Jan. 16, 2003), but provides an alternate approach to the preparation of hydroquinones and 4,4xe2x80x2-dihydroxybiphenyls which eliminates the need for hydrolytic conversion of a p-bromophenol intermediate into the corresponding hydroquinone.
Furthermore, previous methods for the production of hydroquinone and 4,4xe2x80x2-biphenol have focused on the optimization of individual processes for each of the monomers. However, in order to reduce investment-related manufacturing costs at low production volume, it would be advantageous if the subsequent conversion of the benzoquinone could be conducted in the presence of the p-bromophenol intermediate, thus reducing the manufacturing cost of each of the desired products. Furthermore, it would be economical if the reagents used in the processes could be recycled to prepare additional intermediates. The present invention meets these needs.
In one aspect, the present invention provides a method preparing a mixture of a p-bromophenol and a p-benzoquinone. The method comprises contacting in a reaction mixture a hydroxyaromatic compound with:
(a) hydrogen bromide;
(b) at least one source of copper selected from the group consisting of copper compounds, and elemental copper; and
(c) oxygen gas;
The hydrogen bromide is present in an amount corresponding to less than 0.2 moles of hydrogen bromide per mole of the hydroxyaromatic compound, and the contacting takes place at a temperature ranging from about 20xc2x0 C. to about 250xc2x0 C.
In another aspect, the present invention relates to a method for the preparation of hydroquinones and 4,4xe2x80x2-dihydroxybiphenyls. The method comprises conversion of a mixture of a p-bromophenol and a pbenzoquinone into purified forms of the corresponding 4,4xe2x80x2-dihydroxybiphenyl derivative and the corresponding hydroquinone derivative.
In another aspect, the present invention provides a method for preparing a mixture of a p-bromophenol and a 1,4-hydroquinone derivative. The first step of the process comprises contacting in a reaction mixture the hydroxyaromatic compound with hydrogen bromide, oxygen gas, and a source of copper selected from the group consisting of copper compounds and elemental copper at a temperature ranging from about 20xc2x0 C. to about 250xc2x0 C., wherein hydrogen bromide is present in an amount corresponding to less than 0.2 moles of hydrogen bromide per mole of the hydroxyaromatic compound. The product mixture comprises a p-bromophenol, a 1,4-benzoquinone derivative, and the source of copper. In the second step, additional hydrogen bromide and water are added to the product mixture of the first step to produce an aqueous phase comprising the source of copper, unreacted hydrogen bromide, and water, and an organic phase comprising the p-bromophenol, and the 1,4-benzoquinone derivative. The aqueous phase is separated from the organic phase. The third step comprises contacting the separated organic phase with a metal catalyst and hydrogen gas to produce a resulting mixture comprising the p-bromophenol and the 1,4-hydroquinone derivative.